1. Field of the Invention
This invention relates to a system for distributing broadcasting material, such as program material and advertising commercial material, from a source station to at least one branch station, and to such a source station per se and such a branch station per se.
2. Description of the Prior Art
In a television broadcasting network, there is a need to be able to distribute broadcasting material, which is produced and edited in a central source station, from the source station to one, and more usually a multiplicity of, branch stations, so that the same material can be broadcast simultaneously over a large area. The material to be distributed will usually contain a series of commercial material segments, a series of program material segments, or a mixture. Obviously, one possible method of distributing the material would be to transport video cassettes containing the broadcasting material segments, for example by mail or courier. However, it will be appreciated that this would be slow and expensive. Another possible method of distribution is to transmit a series of broadcasting material segments via a space satellite to the branch broadcasting stations. This has the advantage of almost instantaneous distribution, and although satellite time may be expensive, the series of broadcasting material segments may be distributed during off-peak periods. A disadvantage of a simple distribution method of this type is that, at each branch station, it is necessary for an operator to determine the beginning and end of each broadcasting material segment in the series before copying the broadcasting material segment to individual video cassettes which are filed away and which can then be retrieved and broadcast in a desired order. This is a time consuming operation. In order to overcome this problem, it may be considered expedient to synchronise the transmitting operation at the central broadcasting station with the receiving and filing operations at the branch stations. However, a problem arises when using distribution via space satellites, in that space satellites are usually designed to use their own clock signals to control their re-transmission operations. Therefore, although the central and branch broadcasting stations can be synchronised, and the central broadcasting station can transmit the broadcasting material segments to the satellite at desired times, the re-transmission by the satellite to the branch stations will not be synchronised.